Electrodynamic Forces between Electrical Conductors and Cylindrical Magnetic Shields

Aims: This paper demonstrates a method for calculating electrodynamics stress in single-phase and three-phase isolated conductors. Conductors are coated with a cylindrical shield made out of the material containing a magnetic parameter. Special emphasis is placed on induced eddy current of a shield and its effect on reduction of electrodynamics stress of three-phase conductors.

Methodology: The paper starts with the assumption that the cylindrical structure of the conductor shield is infinitely long σ=0. Inside and outside the shield applies Laplace differential equation for the magnetic vector potential [1,3]. Short circuit currents flow through the three eccentric positioned conductors and create magnetic induction or fluxes in a cylindrical shield. AC power corresponds to the time-varying resulting flux that induces eddy currents in the cylinder. Needed values of induction and fluxes relevant to eddy currents and electrodynamics forces can be determined by a method which is based on the calculation of the magnetic vector potentials and Poisson differential equation, A=µJ [2,4,5]. This procedure requires the establishment of a large number of boundary conditions and taking into account the superposition of multiphase conductive structure values. The impact measure of eddy currents in such an eccentric three-phase structure can be determined by using a similar simple procedure which one of the authors applied in the [6-17].

Conclusion: Electrodynamics forces, according to relationship (32), are significantly lower in shields which encompass only one phase of a conductor due to a protective effect of a shield. Eddy currents, as is demonstrated in this paper, significantly reduce magnetic field intensity produced by currents in conductors. Due to this effect, main electrodynamics forces in one-phase structures with shields, don`t affect the conductor but only affect the shield.